Unexamined Japanese Patent Publication No. 2003-274496 discloses a device for setting acoustic characteristics of audio reproducing apparatuses in response to a placement of speakers in a vehicle and characteristics of the speakers. The disclosed device is an acoustic field setting device which provides the audio reproducing apparatus with a network interface or a card interface, and characteristics data of the speakers or information about the placement of the speakers in the vehicle are supplied from the outside of the vehicle, so that an optimum acoustic characteristics can be set.
However, the foregoing document does not disclose a specific method of determining the placement of the speakers in the vehicle, and all the speakers installed are connected to a single audio reproducing apparatus, then the acoustic characteristics of each one of the speakers are determined.
The vehicle recently has encountered two problems, namely, (a) increasing weight due to an increment of harness and (b) a lack of space to accommodate the increased harness. A conventional in-vehicle communication system employs active speaker units which integrate audio reproducing apparatuses with speakers for saving the electrical wiring. This configuration however needs software appropriate for each one of the speakers in order to set acoustic characteristics proper to the respective speakers. Some in-vehicle network needs providing the respective audio reproducing apparatuses with an address in advance, so that the speakers are obliged to have different product numbers from each other because they integrate different software although they look like identical ones.